1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method for reproducing from an image signal a visible image on a recording medium, and a computer readable information recording medium storing therein a program for controlling operation of the image forming apparatus.
2. Description of the Related Art
An image forming apparatus, processing an image signal to form a printed image on a recording medium such as a printing paper sheet or such, is practically used in a copier, a facsimile machine, a printer, or in a MFP (Multi-Function Peripheral), which has functions of a copier, a facsimile machine, a printer and a scanner in a single machine. For example, Japanese Laid-Open Patent Application No. 2000-316063 discloses an image processing apparatus or an image forming apparatus which reads an image from a scanner, and reproduces the image on a printing paper sheet.
FIG. 17 shows a block diagram of such an image forming apparatus.
The image forming apparatus shown in FIG. 17 includes a reading unit 101, a sensor board unit (hereafter referred to as SBU) 102, compression/decompression and data interface control part (hereafter referred to as CDIC) 103, an image processing processor (hereafter referred to as IPP) 104, a video data control part (hereafter referred to as VDC) 105, and an image forming unit 106.
The reading unit 101 optically reads an original (i.e., an original image). The SBU 102 converts an electrical signal obtained from the original by means of a photosensitive device (in this embodiment, a CCD) of the reading unit 101, into a digital signal, and outputs the same. The CDIC 103 controls transmission of image data between respective functional devices and data buses. The IPP 104 corrects signal degradation possibly occurring in the optical system and signal degradation (referred to as signal degradation in the scanner system) possibly occurring in quantization to obtain the digital signal. The VDC 105 carries out dot re-arrangement and pulse control. The image forming unit 106 forms a printed image on a printing paper sheet.
Further, the image forming apparatus includes a process controller 111, a RAM 112 and a ROM 113. The process controller 111 controls a flow of image data transferred through a CPU bus 110. Further, the image forming apparatus includes an image memory access control part (hereafter, referred to as IMAC) 121, a memory module (hereafter, referred to as MEM) 122, an external personal computer (hereafter, referred to as PC) 123, a facsimile control unit (hereafter, referred to as FCU) 124, a public telephone line/network (hereafter, referred to as PN) 125, a system controller 131, a RAM 132, a ROM 133 and an operation part 134.
The IMAC 121 carries out access control for image data to a main memory, extension of data for printing, and compression/decompression of image data for effectively utilizing memory resources. The MEM 122 acts as the main memory. The system controller 131 is connected with the IMAC 121.
The image signal converted into an electrical signal by the CCD of the reading unit 101 is converted into a digital signal as mentioned above. After that, the digital signal (i.e., image signal) is output from the SBU 102. The image signal thus output from the SBU 102 is input to the CDIC 103. Transmission of image data of the image signal between the functional devices and the data buses is controlled by the CDIC 103 as mentioned above. The CDIC carries out data transfer for the image data between the SBU 102, the parallel bus 120 and the IPP 104, and carries out communication of the image data between the system controller 131 and the process controller 111. The system controller 131 carries out total control of the image forming apparatus.
The image data from the SBU 102 is transferred to the IPP 104 via the CDIC 103, corrections of degradation in the optical signal and the degradation in the scanner system are carried out on the image data, and after that, the image data is output to the CDIC 103. The image data thus transferred to the CDIC 103 from the IPP 104 is then transferred to the IMAC 121 via the parallel bus 120 from the CDIC 103. There, under the control of the system controller 131, access control of the image data to the MEM 122, extension of image data given by the PC 123 for printing, and compression/decompression of the image data are carried out. Specifically, the image data thus transferred to the IMAC 121 is stored in the MEM 122 after being compressed, and the data thus stored in the MEM 122 is then read out as is necessary. The thus read data is then decompressed, and then, the image data is returned to the CDIC 103 via the parallel bus 120 from the IMAC 121.
The image data is then transferred to the IPP 104 from the CDIC 103, and after that, an image quality process is carried out. Further, pulse control is carried out by the VDC 105. Then, the image data is sent to the image forming unit 106 which forms a printed image on a printing paper sheet. In this configuration, the parallel bus 120 and the CDIC 103 carry out bus control so that a flow of the image data is appropriately controlled. Thus, the image forming apparatus may act as an MFP.
However, for example, an error of caching of a program or data may occur in the system controller 131. In this case, data access is carried out frequently from the system controller 131 to the main memory 122. As a result, each line data (i.e., the above-mentioned image data) may not be positively transferred to the CDIC 130 within a predetermined writing LSYNC period. As a result, a defect may occur in a printed image formed on a printing paper sheet by the image forming unit 106. It is noted that the above-mentioned LSYNC means, as will be described later, a line synchronization signal, and the writing LSYNC period means a period of successively generated LSYNC for writing.
In consideration of the above-mentioned situation, an object of the present invention is to avoid generation of a defective printed image even when data transfer is carried out frequently to a main memory from a control part, such as the above-mentioned system controller 131, for example.